Tranx groups

Rapid internal triflate displacements by neighboring acetyl or benzoyl groups have been mentioned above when the ester group and the leaving group have tranx-diaxial relationships. This leads to products where the configuration is retained, thus excluding... 

The authors ascribed the ds-stilbene preference to steric interference between the phenyl groups of tranx-stilbene and the phenyl groups on the [Fe -0(TPP+ )]+ intermediate. The Groves research group also gathered the first spectroscopic indications of a synthetic, compound I analog. The [Fe =0(TMP+ )]+ complex (TMP equals the dianion of mexo-tetramesityl-phenylporphyrin) was prepared by the m-CPBA (3-chloroperoxybenzoic acid) oxidation of [Fe -0(TMP)C1]. (See Figure 7.21.)... 

Methyl-2-propenyl)trimethylsilane reacts with cyclohexene at — 10°C for 25 min to give tra ,s-allylsilylated products, tranx-3-(2-methyl-2-propenyl)-6-tri-methylsilylcyclohexene (15%), and tranx-3-(2-methyl-2-propenyl)-4-tri-methylsilylcyclohexene (3%), but no [3 + 2] cycloaddition product. This result suggests that a methyl substituent on the middle carbon of the allyl group prevents the [3 + 2] cycloaddition reaction. 

Substituent-dependent keto enol tautomerism was also observed for 4-piperidin-ones 21 (91ZN(B)1237). When R1 = H, Me, the ketones 21a are more stable than enols 21b, and 2,6-czx-substituted ketones are more stable than 2,6-tranx-substituted ketones. The introduction of an ester group into the 3-position shifts the keto enol equilibrium toward the enol form. 

Their heats of combustion (Table 3.2) reveal that tra i-l,4-dimethylcyclohexane is 7 kJ/mol (1.6 kcal/mol) more stable than the cis stereoisomer. It is umealistic to believe that van der Waals strain between cis substituents is responsible, because the methyl groups are too far away from each other. To understand why tranx-l,4-dimethylcyclo-hexane is more stable than c/x-l,4-dimethylcyclohexane, we need to examine each stereoisomer in its most stable conformation. 

The use of chiral chloroformates, such as that derived from tranx-2-(a-cumyl)cyclohexanol, allows diastereoselective additions to 4-methoxypyridine. The introduction of a tri-ixo-propylsilyl group at C-3 greatly enhances the diastereoselectivity. The products of these reactions are multifunctional chiral piperidines which have found use in the asymmetric synthesis of natural products. ... 

The remainder of the pathway consists of a series of isomerase and group tranx/er reactions (Fig. 11-26). These produce sugar phosphates ranging in size from the 3-carbon glyceraldehyde 3-phosphate to the 7-carbon sedoheptulose 7-phosphate. Also derived from ribulose 5-phosphate is ribose 5-phosphate, an essential component of ribonucleosides and ribonucleotides. The group exchange reactions are catalyzed by transaldolase... 

Conversely, the methyl groups in the cyclopropane derivative of tranx-2-butene are trans to one... 

Addition. Capsinoids. From the fraits of a non-pungent cultivar (CH-19 Sweet) of C. annuum Kobata et al. (1998,1999) could isolate A-free analogues of three major capsaicinoids. They were characterized as esters of vanillyl alcohol and the same fatty acids, which represent the acyl residues in capsaicin, dihydrocapsaicin, and nordihy-drocapsaicin, respectively. Consequently, these esters were named capsiate (vanillyl tranx-8-methyl-non-6-enoate), dihydrocapsiate, andnordihydrocapsiate. Furthermore, the authors proposed the term capsinoids for this novel group of metabolites, which could be detected also in several further cultivars of the species. 

Following the biosynthetic mechanism, initial ionization of GDP to the cation followed by the subsequent addition of the IDP unit forms the FDP cation in a reaction that is catalyzed by FPPS prenyltransferase (Scheme 7.1) [2]. The mechanism is based on the findings that the enzyme, which normally catalyzes the addition of GDP to IDP, is also able to catalyze the hydrolysis of GDP [3]. Deuterium experiments of this hydrolysis process either with D O or with (1S)-[1- H] GDP indicated that C—O bond was broken and the chirality of the C-1 carbon of GDP was inverted in this process. In addition, when trifluoromethyl group was present at the C-3 position or fluoro atom at the C-2 position of the allylic substrate, destabilization of the cation has been witnessed as observed on the retard of enzyme reaction [4]. In the elimination step (Scheme 7.1) hydrogen is removed from C-2 of IDP part with simultaneous formation of a double bond. The formation of a trans or cis double bond during the FPPS reaction depends on the spatial orientation of IDP relative to the elongating FDP. In the tranx-prenyltransferases, the GDP... 

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